Morphological studies of sulfate and nitrate particles on the east coast of North America and over the North Atlantic Ocean

Shipborne and airborne aerosol samples were collected during the Coordinated-Air-Sea Experiment (CASE) over the western North Atlantic Ocean. The experiment was accompanied by measurements on shore near Hampton, Virginia. Individual particle morphology, size, and concentration were analyzed with an electron microscope. Particles containing sulfuric acid, sulfate, nitric acid, and nitrate were identified with various morphological tests. Temporal and spatial variations of aerosol physicochemical characteristics were studied in relation to atmospheric parameters. A diurnal solar radiation effect on concentration and chemical composition of small sulfate-containing particles (0.2 mu m < d < 0.7 mu m) was observed, indicating that the particles are the product of photochemical reaction. Sulfuric acid particles were most frequently observed near noon, and ammonium sulfate particles were dominant at night. The concentration of sulfate particles also depends on air trajectories, including sources of air mass, wind direction, and wind speed. Meteorological conditions (humidity and solar radiation) influenced the concentrations of nitrate-containing aerosols including nitric acid particles. High concentrations of nitrate particles were found only near the source; sulfate particles could transport to greater distances. For both sulfate particles and nitrate particles, concentrations were higher at low altitudes (< 150 m) than at high altitudes (2600 m).